The first confirmed report of stripe rust of wheat for 2023 was received on 7July in southern New South Wales.

Cereal rust pathogens survive from one cropping cycle to the next on living plants (the ‘green bridge’). A scarcity of living susceptible plant hosts over the non-cropping summer months in particular means that cereal rust pathogen populations crash during this time.

Stripe rust of wheat has survived every summer since it was first detected in eastern Australia in 1979. Over the intervening period, it has reappeared sometime between 16 May (1984 and 2008) and 5 October (1994), with the overall average being 23 July. In general, years with the most severe epidemics have been those with the earliest first detection.

The detection of stripe rust on 7July this year was about nine weeks later than in 2022; then, it was first detected on 20 May and one of the worst stripe rust epidemics experienced in eastern Australia ensued.

Reports of stripe rust after the first detection this year have come from Bethungra, NSW (14 July); Tubbul, NSW (20 July); Smeaton, Victoria (20 July); Naracoorte, South Australia (24 July); and Cressy/Longford, Tasmania (26 July).

The broad geographic spread of these locations strongly implicates independent over-seasoning, with the expectation that should conditions favour stripe rust over the coming months, it will ramp up faster than it would have if it had survived at fewer locations.

We are currently processing the stripe rust samples received, with pathotype results anticipated in the next week or so and posted to our regularly updated pathotype distribution map that can be accessed via our website.

Pathotype dynamics

While pathotypes 198 E16 A+ J+ T+ 17+ and 239 E237 A- 17+ 33+ were common in 2022 (63 per cent of all pathotype identifications), pathotype 238 E191 A+ 17+ 33+ increased in frequency from 2.3 per cent in 2021 to 36.4 per cent in 2022.

We first detected this pathotype in 2021. Since then, our greenhouse tests have not revealed any obvious reason for this increase in frequency, as it does not appear to be associated with any obvious ‘breakdown’ in the resistance of any specific variety. Research is continuing to understand this rust pathotype; it is of great interest to see how it behaves in season 2023.

Pathotype distribution determines varietal response

Varietal response to rust is driven by the pathotype or pathotypes present. Long-term nationwide annual surveys of the virulence of the cereal-attacking rust pathogens have been critical in understanding and predicting the responses of cereal varieties to rust diseases and providing direction for resistance breeding.

For example, the separation of the eastern and western Australian cereal belts, the common movement of rusts from west to east, and the less-common movement of rusts from east to west, have resulted in some important pathotypes (and hence virulences) being restricted to eastern Australia.

Monitoring the occurrence, frequency and distribution of pathotypes of the cereal rust pathogens is foundational in genetic approaches to control these diseases. Please send rusted cereal samples using the details below.

The success of our rust surveys depends entirely on the samples received for analysis – so, as always, growers and other stakeholders are encouraged to monitor crops closely for rust in the coming season, and to forward freshly collected samples in paper only to the Australian Cereal Rust Survey, at the University of Sydney, Australian Rust Survey, Reply Paid 88076, Narellan, NSW, 2567.

More information: See an interactive map showing the distribution of rust pathotypes.